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post #1 of (permalink) Old 01-03-2019, 11:57 AM Thread Starter
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Odd injector cup problem

Hey everyone,

I have been chasing down some gremlins in my engine and I think I have finally figured out the whole story. I posted a thread not too long ago about a misfiring engine and an injector not sealing. I am in the process of replacing all of my injectors and decided I should replace the #7 cup since I had an injector fail to seal twice (or so I thought!).

Check this out for a wacky story:

In late 2015, I was moving from Connecticut to San Diego. I had dropped a load of stuff off at my sister's house near Houston since I was not taking it all the way to California. I headed back to Connecticut and started smelling raw diesel when I was driving through Baton Rouge. I had some bad injector cups that were leaking fuel into the cooling system, so I had to get all the cups replaced at a dealership since I was 1800 miles from home with no tools and few options. The dealership replaced all 8 cups. I noticed a little bit of smoke coming from the tailpipe on the way home, but figured it was due to some air in the high pressure oil system and it would eventually work its way out.

The tailpipe smoke never went away, so I started digging into the problem about 18 months after the cup replacement. A buzz test revealed that the #7 injector sounded a bit muted and weak. I pulled the #7 injector and found a blackened end along with several small pieces of metal in the bottom of the cup. I assumed the copper washer fell off the injector during installation and the heat melted the washer. I cleaned out the cup, assumed all was well, and installed a new injector. The smoke cleared up and everything seemed fine. Drove the truck for another 18 months or so without any problems, including a cross-country move from San Diego to New Hampshire (the Navy seems to like for me to move back and forth between opposite corners of the country).

A few weeks ago, my truck started misfiring really bad and would barely run. All signs were pointing to the injectors, so I decided I would just go ahead and replace all of them, even though they only have about 140,000 miles on them. I pulled the #7 injector and found a blackened end - this time much worse than the first time. There was scaly black carbon covering the lower part of the injector (the entire area below the lowest o-ring). Due to another injector sealing problem, I figured the cup was damaged and should be replaced.

I pulled the cup today and got a whole cup minus the bottom flat part (with the hole) that seats against the head. I figured crap - the bottom of the cup broke off, so I tried to figure out how to get just the bottom of the cup out of the bore in the head. After cleaning up the bore really well, I noticed that the bottom of the bore looked like cast iron instead of brass. I wondered what in the world happened the to the bottom of the cup. Then it hit me - I bet those melted pieces of metal that I found 18 months ago were actually the bottom of the cup and not parts of a copper washer. Turns out I was right - I still had the little melted pieces (don't ask me why I kept them, but I'm glad I did) and looking at them, they are definitely brass and not copper. This would explain why the new injector did not seal - there was no cup bottom to seal to!

At least I don't have to try to fish the bottom of a cup out of the head. Just need to clean up the bore and press a new cup in now.

To sum it up, my new theory is that the dealership installed the #7 injector without a copper washer (probably fell off during the installation process and the mechanic failed to notice). This resulted in the #7 injector not sealing at all, and the heat from the combustion gases melted the bottom of cup (that's the pieces of metal I found). I installed a new injector, but it also did not seal since the bottom of the cup was missing. I basically had the same thing happening again, and the bottom o-ring finally lost its ability to hold back the cylinder pressure and combustion gases.

I also might have found another potential cause of the misfire. My ICP connector had some oil in it, so that probably messed with the ICP signal. ICP looked fine when I monitored it with AE, but I only watched it for a few minutes. New ICP sensor is on the way.

I figure that's probably the craziest injector cup story anyone has ever heard. You can't make this **** up!
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